September 28th 2024.
A team of researchers from IIT Bhubaneswar, University of Southampton, National Oceanography Centre, and Stockholm University have delved into the intricate workings of the Atlantic Meridional Overturning Circulation (AMOC). This circulation is a crucial factor in regulating the Earth's climate and plays a significant role in maintaining the relatively mild temperatures in northern Europe, including the UK, despite its high latitude.
The team's findings, published in 'Nature Communications', have shed light on the vital role that the mixing of Atlantic and Arctic waters plays in sustaining the AMOC. According to lead author Dipanjan Dey from IIT Bhubaneswar, the AMOC functions like a vast conveyor belt, transporting warm tropical water northward and cold water southward, effectively distributing heat globally.
Through their research, the team discovered that 72% of the AMOC's lower limb consists of Atlantic waters, while the remaining 28% is made up of Arctic waters. As warm water from the Atlantic reaches cooler regions in the North Atlantic, it loses heat, becomes denser, and sinks. Dey explains that much of this dense water then travels northward, mixing with colder Arctic waters before flowing back southward, ultimately strengthening the AMOC.
The study also challenges prior assumptions that focused primarily on heat loss as the main driving force behind the AMOC's strength. It estimates that the mixing of Atlantic and Arctic waters accounts for a significant 33% of the transformation of warm water into denser, colder water, with the remaining 67% driven by ocean-atmosphere interactions.
As our planet continues to warm, models predict that the AMOC may weaken, potentially leading to significant shifts in global climate patterns. These new findings offer valuable insight into how the mixing of Atlantic and Arctic waters affects climate dynamics. Dey also points out the relevance of this research in the Indian context, particularly regarding climate change.
He explains that the Indian summer monsoon, which brings in 80% of the country's annual rainfall, is a vital factor in agriculture, the economy, and public health. Any changes in the timing or distribution of this rainfall can have far-reaching impacts, both physically and mentally. For over 300 years, it was believed that the monsoon resulted from large-scale land-sea breezes driven by temperature differences. However, satellite imagery in the 1980s revealed that cloud patterns over India closely resemble the Inter-tropical Convergence Zone (ITCZ), a low-pressure zone near the equator.
This discovery redefined the monsoon as a seasonal migration of the ITCZ from the ocean towards land, rather than a simple land-sea breeze. According to Dey, the northward flow of warm water in the AMOC plays a crucial role in maintaining the ITCZ's position just north of the equator. However, with a warming climate, the AMOC is predicted to slow down, reducing the northward movement of warm water and energy. This could potentially shift the ITCZ southward, weakening the Indian summer monsoon in the future.
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